The present invention relates to a device for fastening a needle case to a yoke for use in universal joints of the trunnion type, and more particularly to such a device useful in universal joints having a limited swing diameter.
With universal joints heretofore known in which the needle case is adapted to be fastened to the yoke by two bolts, a key of simple shape on the surface of the needle case to be joined to the yoke is merely engaged in a keyway of identical shape formed in the surface of the yoke to be joined to the needle case, and the needle case and the yoke are fastened together by the bolts.
During the transmission of torque, the needle case A shown in FIGS. 1 and 2 is subjected to a tilting torque which is the product of torque F of the universal joint multiplied by distance h from the joint surface to the center of the trunnion, i.e., F .times. h. The tilting torque, which acts to tilt the needle case A on the joint surface of the unillustrated yoke, is to be received not by the bolt B but by the joint of the key C and keyway (not shown). However, if there is a clearance between the key C and the grooved portion of the yoke, tension P = Fh/(X + Y) will act on the fastening bolt B. Accordingly, the bolt must possess a fastening force sufficient to tightly hold the needle case to the yoke in intimate contact therewith during the transmission of torque against the tilting torque. Invariably, therefore, there is a tendency to use a bolt of large diameter.
It is noted that the universal joint shown in FIG. 1 has a limited swing diameter D.sub.0 which in turn limits the maximum width L of the needle case A. If it is then attempted to increase the size of the bolt B without altering the torque capacity of the universal joint, the diameter d of the bolt hole shown in FIG. 2 increases, consequently reducing the thicknesses .delta. and H on the joint surface of the portion of the needle case A defining the bolt hole. Thus there is the likelihood that the fastening force of the bolt B and the transmitted torque will deform the needle case A.
The reduction in the rigidity of the needle case will reduce the life of the universal joint and result in needle case fracture. Consequently, the combination of an increased bolt size and a sufficiently rigid needle case can be achieved only by decreasing the race diameter D.sub.1 of the needle case A. This leads to a reduction in the diameter D.sub.2 of the trunnion and a reduced torque capacity.